U.S. Pat. No. 7,046,228 discloses an electrophoretic display device having a dual switching mode which allows the charged pigment particles in a display cell to move in either the vertical (up/down) direction or the planar (left/right) direction. In such a display device, each of the display cells is sandwiched between two layers, one of which comprises a transparent top electrode, whereas the other layer comprises a bottom electrode and at least one in-plane electrode. Typically, the display cells are filled with a clear, but colored dielectric solvent or solvent mixture with charged white pigment particles dispersed therein. The background color of the display cells may be black. When the charged pigment particles are driven to be at or near the transparent top electrode, the color of the particles is seen, from the top viewing side. When the charged pigment particles are driven to be at or near the bottom electrode, the color of the solvent is seen, from the top viewing side. When the charged pigment particles are driven to be at or near the in-plane electrode(s), the color of the display cell background is seen, from the top viewing side. Accordingly, each of the display cells is capable of displaying three color states, i.e., the color of the charged pigment particles, the color of the dielectric solvent or solvent mixture or the background color of the display cell. The dual mode electrophoretic display, according to the patent, may be driven by an active matrix system or by a passive matrix system.
U.S. application Ser. No. 12/370,485, filed Feb. 12, 2009, discloses a display device which utilizes a brightness enhancement film or black matrix layers to achieve an alternative color structure. By a post scanning method, the electrodes of the active matrix can be addressed. The enhancement film or black matrix layers can hide the charged pigment particles at the black state, without sacrificing the overall light efficiency.